<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>Document</title>
</head>

<body>
     <form id="form1">
        <p>
             <label for="tel">手机号</label>
             <input type="tel" name="tel" id="tel">
        </p>
        <p>
             <button type="submit">提交验证手机号</button>
        </p>
    </form>
</body>
<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.6.3.js"></script>
<script>
    $("#form1").submit(function (e) {
        let tel = $("#tel").val();

        let reg = /^1[3456789]\d{9}$/;
        if (reg.test(tel)) {
            alert("手机号合法")
        } else {
            alert("手机号不合法")
        }
        return false;
    })
</script>

</html>